Extradition is diplomatic, political and legal. Its purpose is to ensure that those who are alleged to have committed serious crimes within one legal jurisdiction cannot escape prosecution by simply moving to another. Two principles underpin the proper approach to extradition.

First, the obligation on any government to ensure that the rights of its citizens both at home and abroad are protected. Second, that it is in the interests of all of us that criminal behaviour wherever it is committed should be prosecuted. In abstract these principles seem unexceptionable but in practice they have the potential to cause a serious diplomatic, political or legal clash. Any such clash damages the confidence of the public in extradition.

A clash has arisen between the United Kingdom and the United States, which is why Nick Clegg asked me to review the issue of extradition.

What makes the clash particularly disturbing on both sides of the Atlantic is that it arises as a result of a treaty entered into by the Blair government and the Bush administration in the aftermath of 9/11 with the understandable purpose of making the transfer of alleged terrorists between the two countries as effective and efficient as possible. The British Parliament quickly ratified the treaty and passed the necessary consequential domestic legislation. The American Senate, which has the power to ratify treaties, delayed under the influence of the Irish lobby, but ultimately did so. A treaty between close allies with a common interest in dealing expeditiously with terror suspects might be thought to be an ideal way in which to regularise these matters. But unhappily this has not been the effect in this case.

The most controversial element arises from the fact that in accordance with the Fourth Amendment to the US Constitution, "probable cause" has to be shown before a UK request for extradition of an American citizen will be granted. For British citizens the reciprocal test is "reasonable suspicion". That these tests embody different standards to the disadvantage of United Kingdom citizens was accepted by the Blair government during the ratification process, though now it appears that one of those responsible has departed from that view. The Baker Inquiry established by Theresa May reached the conclusion that that there was no practical difference between the two tests. With that conclusion I respectfully disagree. To put the matter as simply as I can one may have a "suspicion" that someone has committed a crime but that is a different and lower standard than being satisfied that it is "probable" that a crime was committed by that person. The proper course should be to raise the British standard to the American one so that UK citizens do not suffer a disadvantage compared to their US equivalents.

If the present British government is to fulfil its duty to protect the rights of its citizens at home and abroad, and at the same time meet its treaty obligations, such a change is both necessary and possible, not least to restore public confidence in Britain in the process of extradition between the United States and the United Kingdom.

But it seems necessary to go further. An act committed in one country may produce consequences in another. Questions may then arise as to where the alleged criminal should be prosecuted. At present that decision is taken in the United Kingdom by the prosecuting authorities and in private. In the interests of transparency and proper recognition of the rights of UK citizens the decision should be taken by a judge in open court. It is argued that such a procedure, which is commonly called "forum bar", would delay the outcome of proceedings for extradition. And a similar objection is made to the requirement that prima facie evidence should be available to a court when extradition is sought.

But accepting such requirements would fulfil the responsibility of the British government to protect the human rights of its citizens at home and abroad, a responsibility which it shares with Parliament.

A further argument worth consideration is whether the penal consequences of extradition, prosecution and conviction such as the length of any sentence and the conditions in which it may be served should be taken into account.

It must surely be right that the courts in this country should not be obliged to prioritise the principle of mutual recognition which underpins the concept of extradition to such a degree that the threshold for resisting extradition on human rights is set at a level which effectively deprives a person of any human rights protection at all.

Both the United States and the United Kingdom have a common interest in resolving these issues in such a way as to preserve the effectiveness of extradition while ensuring its fairness in operation.